1. Field of the Invention
The present invention is generally in the field of digital image processing. More specifically, the present invention is in the field of CMOS imager systems for digital image capture and image processing.
2. Related Art
Mobile imaging devices, such as cell phone cameras, require very small size cameras to capture a target scene and output an image that corresponds to the target scene. As pixel resolution is increased and camera size is held constant or reduced in mobile imaging devices, the pixel size for imagers, such as complementary metal oxide semiconductor (CMOS) imagers, in the cameras is reduced. As a result of pixel size reduction, the dynamic range of the image provided by the CMOS imager is also reduced, which can cause degradation of outdoor image quality.
In one conventional approach, the dynamic range of the image provide by the CMOS imager can be increased by combining two or more independent frames together, where each frame is produced at a different exposure. For example, a first frame can be produced at a first exposure and stored in a frame buffer. A second frame, which is produced at a second exposure, can then be combined with the first frame in real time by utilizing a digital process. However, this approach requires the storage of one full frame of data in a frame buffer prior to processing the second frame, which significantly increases the cost of the camera system.
The dynamic range of the image provided by the CMOS imager could also be increased by utilizing larger pixels with increased capacity. However, increasing pixel size undesirably increases the manufacturing cost of the imager and, consequently, the cost of the cell phone camera or other mobile imaging device in which the imager resides. In addition, the physical size limits of portable electronic devices often do not allow an increase in the size of the camera which must accompany the use of a larger pixel element.
Thus, there is a need in the art for a small, cost-effective camera system, such as a CMOS imager with small pixel, that can provide an image having increased dynamic range.